Automatic boiler-control apparatus



Sept. 21, 3926. 1,600,964 L. w. THOMPSON AUTOMATIC BOILER CONTROL APPARATUS Filed April 10, 1926 1,111,11 nvllllllll yllllni llllll Inventor: Louis Thompson His Attorney.

Patented Sept. El, 192%.

UNHTED STATES when PATENT @FFHCE.

LOUIS W. THOMPSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELEC- TRIO COMPANY, A CORIiORATION OF NEW YORK.

AUTOMATIC BOILER-CONTROL ATPARATUS.

Application filed April 10, 1926. Serial No. 101,218.

The present invention relates to automatic boiler control apparatus, and more particularly to electrically operated apparatus of this character,

The usual electrically operated boiler control apparatus heretofore provided has been complicated and has required constant attention in operation because of numerous intermediate relays required to carry out an effective cont-r01 scheme and the numerous contacts involved thereby.

The object of the present invention is to provide an improved and simplified electrically operated boiler control apparatus wherein intermediate relays and their contacts are eliminated and whereby the fuel and air supply to a boiler are automatically varied in accordance with the demand upon the boiler and in definite relation to the amount of variation of boiler pressure.

For a consideration of what is believed to be novel and the invention, attention is now directed to the accompanying drawing, the description thereof, and the appended claims.

In the drawing, Fig. 1 is a diagrammatical illustration of a boiler provided With control apparatus embodying the invention, and Fig. 2 is a view, on a greatly reduced scale, of a boiler installation. to which the apparatus of Fi 1 is adapted.

Referring to the drawing, 5 is a ower plant boiler and furnace having a fuel eeder of any suitable character, such as a stoker 6 driven by an electric motor 7 and a forced draft fan or blower 8 driven by a second electric motor 9. The boiler is to be taken as representing any elastic fluid or vapor generating plant comprising one or more units, asingle unit with its draft and fuel supply being considered sufficient to illustrate the use and operation of the control means of the present invention without complicating the description or the understanding thereof. The arrangement is such that the draft and fuel supply and the elastic fluid output of the boiler or plant are increased by increasing the speeds of motors 7 and 9 and decreased by decreasing the speeds of motors 7 and 9.

In the present example the motors are of the shunt-wound direct-current type and are controlled by means of a field rheostat 10 common to both of them as a convenient and simple means for controlling their speeds simultaneously, although other motor means rheostat 10 and a common draft and fuel control circuit 14 in which the rheostat is located, thus providing a simple, effective, simultaneous control means for both motors and for the elastic fluid output of the boiler.

Rheostat 10 is provided with the usual moving contact arm 15 by movement of Which' its resistance is varied and in the present example is operated by a reversible electric motor 16 connected with the arm through a worm and wheel drive arrangemeut indicated at 17. Together with motor 16 it represents any suitable control means by which the draft and fuel supply to the boiler is varied.

As is Well understood in connection with the field control of shunt motors as shown,

decreasing the field strength causes the mo-' tors to increase in speed and increasing the field strength causes a corresponding decrease in speed. Rheostat 10 is shown in its full speed position wherein arm 15 has moved to place the full resistance in the field control circuit, thereby fully decreasing the field strength of both motors and causing them to operate at full speed.

Motor 16-is of the alternating current type and is provided with the Well known split field indicated at 18 and 19, field 18 being employed to drive the motor to move the rheostat arm clockwise toward the low speed position and field 19 being employed to drive the motor to move the rheostat arm counter clockwise toward the high speed position adjacent which it is shown.

Both field sections are joined at 20 and connected with one of a pair of alternating current supply mains 21 through a common circuit wire 22, while their opposite terminals are connected Witlrthe other of said mains 21 through separate circuit or control wires 23 and 24. Circuit wires 23 and 24, together with circuit wire 22, provide a-divided control circuit. In circuit wires 23 and 24 are located variable impedances 25 and 26 respectively. The motor armature is connected with supply mains 21 through a feeder circuit 27 in which is located a speed control means represented by a series connected rheostat 28.

This arrangement differs from the usual split field reversing arrangement in that both field sections 18 and 19 are energized simultaneously, and when both impedances 25 and 26 are equal, it will be seen that the fields will equally oppose each other and prevent the motor from operating the rheostat or control means for the fuel and draft motors 7 and 8. Any unbalance in the values of the impedances will cause a corresponding unbalance in the current flow in the opposing field sections and operation of the motor in one direction or the other, depending upon which field section becomes the stronger. The present arrangement is such that with a given setting of impedance 26 for a balanced condition between it and impedance 25 for non-operation of motor 16, a decrease in the value of impedance 25 causes the current flow in field section 18 to become the stronger and the motor then operates to move rheostat arm 15 toward the low speed position, that is, clockwise as viewed in the drawing, while an opposite unbalance between the impedances causes an opposite movement of the rheostat arm.

To prevent overtravel of the rheostat arm in either direction, limit switches 23 and 24 are arranged to be operated by it when in the extreme full and low speed positions,

limit switch 23 for this purpose being inserted in circuit Wire 23 and limit switch 24 being inserted in circuit wire 24.

With the arrangement thus far described, it will be seen that the fuel and draft supply for the boiler and its elastic fluid output may be increased or decreased by varying one of the impedances 25 or 26 with respect to the other, and that the fuel and draft supply and output remain constant while the impedances remain balanced or equal. By placing one of the impedances under control of a variable quantity associated with the operation of the boiler, such as the boiler pressure for example, this arrangement provides a simple and effective means for controlling the fuel and draft supply and the elastic fluid output of the boiler in accord.- dance with changes in the value of said quantity.

In the present example, the boiler pressure or the pressure in a main boiler header is made to control the fuel and draft through the use of a pressure regulator or pressure responsive means 29 of any suitable type connected with impedance 25 by a control circuit 30.

The pressure responsive means 29 is preferably in the form of a pressure gauge of the same general type as the flow meter described in the patent to Thompson & Mc- Nairy, No. 1,560,951, filed November 10, 1925, and comprises a mercury chamber 31 in which is located a transformer core provided with a primary winding The later is connected with circuit wires 30 to control impedance 2:). In the present ex ample in'ipedance 25 is a step down or current transformer having a primary 34 connected in control wire 23 and a secondary 35 which supplies low voltage to the primary 33 of the gauge through circuit wires 30.

The trailing pressure pipe of the gauge, indicated at 36' is connected to atmosphere while the leading pressure pipe 36 is clongated to form a vertical stand pipe or pressure column between the gauge and a reservoir 37 which, together with the pipe, is filled with mercury as indicated at 38. The reservoir is in turn connected through a pressure pipe 39 with a main header 40 of the boiler plant to which the boiler is connected through a delivery main 41. The gauge is thus supplied with pressure from the main header of the plant through the reservoir and stand pipe connection and operates in response to a differential pressure between atmosphere and said pressure.

The height of the stand pipe 36 is such that the mercury column therein sets up a back pressure sufiicient to balance the differential pressure corresponding to normal boiler pressure whereby the mercury assumes a certain normal level in chamber 31.

Viewed in another aspect, the arrangement is such that pipes 36 and 39 form a U- tube connection between the gauge and header 40, pipe 39 forming one leg thereof and pipe 36 and chamber 31 the other. The pressure in header 40 maintains a head of mercury in pipe 36 and chamber 31, and as the pressure in said header increases and decreases, the mercury rises and falls in chamber 31 in proportion thereto.

The mercury in chamber 31 surrounds the core 32 and forms a short circuited secondary therefor of decreasing and increasing resistance 'as it rises and falls in response to changes in boiler pressure. The gauge thus forms a variable load on secondary 35 and as the mercury column rises and falls the variable load causes the impedance of the transformer primary 34 todecrease and increase, a higher mercury level resulting from a higher pressure causing the impedance to decrease proportionately and a lower mercury level resulting from a lower pressure, causing the impedance to increase proportionately.

Such changes in impedance cause the m0- tor control circuits 23 and 24 to become unbalanced and effect corresponding movement of the rheostat arm 15 in the manner hereinbefore described. The circuits are balanced for any impedance value of impedance 25 correspondlng to a desired boiler pressure, by adjusting impedance 26 with respect thereto. In the present example, impedance 26 is indicated as being a simple variable resistance, although any suitable variable impedance may be used,

In the initial adjustment of the apparatus, the control rheostat 10 is set to provide a certain speed for motors 7 and 9 whereby the normal desired boiler pressure or pressure in the header is set up with normal load or elastic fluid demand on the header. The normal pressure causes the mercury level in chamber 31 to assume a certain height and a corresponding impedance value is established thereby in rheostat control wire 23 by the load on transformer 25. This impedance value is balanced in rheostat control wire 24 by adjusting rheostat 26. Rheostat motor 16 then remains stationar An increase in the pressure from t e normal value, caused by a decrease in demand for elastic fluid for example, then causes a proportional rise in the mercury level, an increase in the load on transformer 25 and a proportional decrease in the impedance in primary 34 and control wire 23,- with the result that field 18 becomes more strongly energized than field 19, whereupon the motor moves to operate rheostat arm 15 in a direction to decrease the speed of the draft and fuel motors, that is, clockwise as viewed in the drawing, and correspondingly decreases the pressure and the elastic fluid output. As soon as the pressure falls to normal as a result of the decreased fuel and draft supply, the mercury level in chamber 31 and the corresponding load on transformer 25 fall proportionately, until the impedance of the latter balances impedance- 26 whereupon motor 16 is stopped.

Likewise a decreasein the pressure from normal for any reason causes field 19 to become the stronger and motor 16 to move rheostat arm 15 to increase the speeds of the fuel and draft motors. In the present example, the apparatus is shown as opprating with such decreased pressure. In t is case the pressure has fallen to a minimum low value as indicated by the low mercury level in chamber 31. This causes the impedance of transformer 25 to reach a maximum or substantially no load value, under which condition field 18 is greatly weakened with respect to field 19, whereupon the motor operates to move the rheostat arm toward the high speed position adjacent which it is shown, as hereinbefore mentioned.

The speed with which motor 16 moves the rheostat arm 15 is regulated by rheostat 28. To a certain extent the setting of rheostat 28 also determines the amount of unbalance permitted in the control circuit before it begins to move in response thereto.

ln conjunction with the mercury pressure suitable type may be inserted in circuit with impedance 25 to indicate or record changes in the current therein as a measure or indi-' cation of changes in the header pressure as supplied by the boiler. Such a. device is indicated by an ammeter 42 having a scale 43, suitably calibrated to read pressure for example, and an indicating pointer 44 which moves over the scale in response to changes in the current flow resulting from changes in the pressure.

From the foregoing description, it will be seen that through the use of the balanced impedance circuit 222324 comprisin impedances 25 and 26 in connection with the split field motor 16, an effective and simplified control means is provided between the pressure gauge or pressure-responsive means 29 and the rheostat or controller means 10 for the draft and field supply of the boiier without the use of delicate, sensitive relays having a multiplicity of contacts as heretofore employed in such control systems.

"With the present arrangement the control circuits are energized at all times and hence It should be understood that while the embodiment of the invention described herein provides only for the control of the fuel and draft of a boiler, the invention is not limited thereto, nor to the particular means shown herein for efiecting control as above pointed out, but may be embodied in any apparatus for the regulation of elastic fluid or vapor generators where simple, rugged, control means providing a definite relation between an operating condition of the generators and the regulation thereof is desired.

What 1 claim as new and desire to secure by Letters Patent of the United States is:

1. The combination with an elastic fluid generator provided with means whereby its elastic fluid output is controlled, of a regulator therefor connected with said control means to operate the same, said re ulator and controlled by the pressure responsive device, a divided control circuit for said first-named means in one leg of which said impedance is located, and a second variable net impedance in the other leg of said divided circuit.

2. The combination with an elastic fluid generator having a variable fuel and draft means by which its elastic fluid output is controlled, of a controller means by which said fuel and said draft means are jointly varied, motor means by which said controller means is operated, a divided control circuit connected with the motor means, a variable impedance in each leg of said divided control circuit, and means responsive to changes in the elastic fluid output of the generator connected with one of said impedances to vary the same.

51. The combination with a boiler, of means connected therewith for varying the fuel and draft supply thereto, a divided electrical control circuit connected with said means, a variable impedance in each leg of said circuit, and a presstire-responsive device connected with the boiler and with one of said impedances for varying the latter in response to changes in the boiler pressure.

4. The combination with an elastic fluid generator provided with means for varying: its elastic fluid output and pressure, of a split field motor connected with said means for ope 'ating the same. a variable impedance in circuit with each side of said field, means for energizing both sides of said field simultaneously through said impedances, a pressure regulator responsive to the elastic fluid pressure provided by said generator, and means providing a connection between the pressure regulator and one of said impedances whereby the latter is varied in remeans for energizing both sides of said h'eld simultaneously, and a variable impedance in circuit with one side of said motor field controlled by said pressure gauge.

6. The combination with a boiler, of a regulating means the'efor which is movable in ne. direct n to increase the supplv f fuel and draft to the boiler and which is movable in an opposite direction to decrease said .fuel and draft supply, an electric circuit connected with said control means, which circuit when energized effects the operation of the control means in said firstnamed direction, a variable impedance in said circuit, means responsive to ressure supplied by the boiler connected with said impedance to vary the same, a second electrical circuit connected with said control means, which circuit, when energized, effects the operation of the control means in the second-named direction and a second variable impedance in said circuit.

In witness whereof, I have hereunto set my hand this 9th day of April, 19:26.

LOUIS W. THOMPSON. 

